應用樹輪生態學方法重建臺灣中部塔塔加地區臺灣雲杉林分動態

Abstract

臺灣位於西太平洋北部之颱風帶，每年颱風季常有颱風挾帶著強風豪雨侵 襲。如此頻繁且規模較大的擾動，對於臺灣森林的動態與演替應扮演極為重要的 角色，然國內迄今未能對此議題有深入之探討。有鑑於此，本研究以樹輪生態學 方法，探討臺灣中部塔塔加地區臺灣雲杉永久樣區之林分動態。經由每木定位及 生長錐鑽取臺灣雲杉、臺灣鐵杉、臺灣華山松樹芯，並透過輪寬量測與交叉定年， 得出雲杉林每木的年齡與徑向生長量。而後依生長變化率以移動平均法、標準界 限曲線法及絕對增加法重建過去擾動年代表，期望瞭解與重建該林分之歷史動態。 結果顯示，本樣區林木最早建立於 1691 年。齡級結構呈雙峰分布，分別於 1760~1850、1870~1930 年有兩個世代的族群建立潮；雲杉與鐵杉的建造歷史相近， 可略分為兩個世代，而華山松的建立較為均勻且少量。在林齡的空間分布上，中 世代(1760~1850)與新世代(1870 以後)有明顯的塊集鑲嵌現象，分別佔據樣區東半 邊與中央偏西北側。 建立雲杉、鐵杉、華山松標準界限曲線y = 816.17e-1.179x、y = 630.67e-0.934x、y = 791.1e-1.276x 以估計樹種反應擾動事件的潛在最大生長變化率；擾動重建結果，不同 準則方法所重建的擾動年代表類似，林木顯示1740’s、1770’s、1850’s、1890’s、1940’s 年代有較大的生長釋放，結合齡級結構、樹齡空間分布與擾動年代表，推測過去 曾於1740’s、1850's 年代發生林分取代性擾動。新世代林木所佔據的區塊，與2009 年莫拉克颱風所所造成之崩塌相符合，推測過去於1850’s 年代可能有類似大規模 地滑事件造成大面積的林地裸露，並於30 年後才開始大量建立；而1740’s 年代也 潛在有大規模擾動事件發生，但時間較為久遠、留存林木較少，可信度較低。 雲杉與鐵杉的生育地相似，過去文獻指出雲杉需要較大的孔隙才有幼苗更 新，崩塌為其可能之更新機制，大規模擾動對於雲杉更新扮演著促進的角色，以 維持其族群優勢。

Typhoon is one of the most important natural disturbances of Taiwan, typically bringing heavy rains and strong winds. However, we have yet to fully understand how such disturbances affect Taiwan’s forest dynamics and successions. The objective of this study is to reconstruct disturbance chronology and to understand the dynamics of a Taiwan spruce (Picea morrisonicola) stand in central Taiwan based on a dendroecological approach. The stand was mainly comporised of Taiwan spruce, with Taiwan hemlock (Tsuga chinensis var. formansa) and Taiwan Masters pine (Pinus armandii var. masteriana) being the co-dominant species. Each tree of the three species within the stand was mapped and cored. Following the standard dendrochronological steps, the age at coring-height of each tree was then determined. By applying the moving-average method, boundary-line method, and absolute-increase method, this study reconstructed the disturbance chronology of the stand. The results suggested that the oldest tree in the stand was established in 1691. The age structure of the stand showed a bi-modal distribution with two cohorts (1750~1850, 1870~1930). The age structures of spruce and hemlock was similar, whereas the establishments of the pine were rare but evenly distributed. Spatially, the two cohorts occupied the eastern (first cohort) and northwestern sides of the stand, respectively. The three methods used to reconstruct disturbance chronology showed similar patterns with major growth releases in the 1740’s, 1770’s, 1850’s, 1890’s, and 1940’s. Based on the age structures, spatial distributions, and disturbance chronology, this study suggested that there were two major stand-replacement events in the 1740’s and 1850’s. As the second cohort (1870~1930) was largely destroyed by the Morakot typhoon of 2009, it is inferred that an event with a magnitude similar to that of the Morakot iv typhoon occurred in the 1850’s. Another significant disturbance event might have occurred in the 1740’s. However, due to limited amount of information, the occurrence and impact of the event were less certain. It has been suggested that Taiwan spruce may require large gaps to regenerate and maintain its dominance in the study area. The results from this study confirmed this hypothesis.